1. Field of the Invention
The present invention relates to a digital video recorder which can write the audiovisual data (e.g., moving pictures, audio data and so on) of a TV broadcast program on a storage medium in real time. As used herein, the “digital video recorder” is not limited to a fixed digital video recorder for use to write broadcast data but may broadly refer to a camcorder, a personal digital assistant or any other mobile electronic appliance.
2. Description of the Related Art
Digital video recorders for writing digital data on storage media such as an optical disc and/or a hard disk have been rapidly popularized recently. Among other things, a hybrid digital video recorder that comprises both an optical disc drive and a hard disk drive (HDD) attracts particularly much attention in the market. Such a hybrid digital video recorder allows the user to write the data to be saved on a hard disk first and then transfer that data from the hard disk to an optical disc, for example. In such a digital video recorder, the hard disk is fixed to the recorder and cannot be removed, but the optical disc can be easily removed. Accordingly, if an arbitrarily selected one of multiple optical discs prepared is loaded into this digital video recorder, then the data on the hard disk can be transferred to the optical disc and saved outside of the digital video recorder any time. Consequently, by using such a hybrid digital video recorder, various types of data (including moving pictures, still pictures and audio data) can be written and stored on the hard disk and/or optical discs.
Most of the optical disc drives included in those digital video recorders has a defect correction function to protect the data to be saved. In the digital video recorders disclosed in Japanese Laid-Open Publications Nos. 2000-100078 and 2000-112672, for example, an alternate area is provided in advance on an optical disc. If the optical disc has any defect, then no data will be written on the defective area and its surrounding areas. Instead, the data to be written there is written on the alternate area. The defect on the optical disc is typically dust or scratch on the disc surface.
By making such a defect correction, nothing will be missing from the information stored due to those defects, and therefore, information can be recorded and saved with high reliability.
Also, when broadcast data should be stored on an optical disc with a hybrid digital video recorder, the data is sometimes temporarily written on a hard disk included in the recorder before being written on the optical disc finally. That is to say, the broadcast data that has been once written on the hard disk is read out thereafter and then written on the optical disc. According to such a writing method, the hard disk is used as a sort of cache memory before the write operation is eventually done on the optical disc. Japanese Laid-Open Publications Nos. 2002-033997 and 2002-150683 both disclose such a technique of using a fixed storage medium in a recorder as a cache memory.
The alternating processing described above works if it is expected that some defects should be present on a given optical disc or while the optical disc drive is too busy with writing data on the optical disc to handle a new request. However, the alternating processing would not be quite effective should some abnormal event happen during the write operation (i.e., if an unexpected write error happens).
Such unexpected write errors typically happen due to tracking errors. The tracking errors are possibly caused due to (1) the presence of some defects on the surface of the given optical disc, (2) some externally applied shock or (3) the poor quality of the optical disc itself (e.g., having a significant degree of eccentricity or warpage).
Recently, demands for write-once optical discs such as DVD-R have been growing rapidly because such optical discs are relatively inexpensive. However, in those inexpensive write-once optical discs, the write errors tend to occur very frequently.
For example, if such a write error happens while a huge amount of data such broadcast cast is being written on an optical disc, then the amount of missing data will be much greater than the storage capacity of a normal alternate area on the optical disc. Accordingly, the conventional defect correcting processing cannot cope with such a big write error. Also, even if the alternate area has a sufficient capacity, it is still a problem that the optical disc drive cannot access the alternate area so frequently as not to miss any part of the data to be saved.
It should be noted that if the optical disc is used as mere backup storage (e.g., as an archive to save the information that has been copied from the hard disk), such problems rarely occur. In that situation, even if the optical disc drive needs to access the alternate area more times, it may take a longer time to complete the backup storage operation. Also, even if the write errors have occurred so frequently and the amount of errors exceeds the capacity of the prepared alternate area, you can insert a new disc and start the backup operation again since the original data is still left on the hard disk as it is.
However, those write errors will give serious effects on broadcast data being received by a TV set, for example, or audiovisual data (e.g., moving picture data and audio data) being captured by a camcorder while the data is being written on an optical disc in real time. These incoming video and audio signals are continuously supplied non-interactively. That is to say, it is impossible to control the operation of the data supplying or transmitting end (i.e., the master) according to the situations of the data receiving and storing end (i.e., the slave). In that case, if a write error occurs during a write operation, the real-time data such as the broadcast data stream will never wait until the alternate process is complete. Accordingly, any halt of the alternating process means missing some part of information to be saved.
It should be noted that most of these problems are avoidable if the broadcast or captured data is not directly saved on the optical disc but cached on the hard disk or a DRAM and then saved on the optical disc. In that case, however, even if the user wants to save the broadcast or captured data on the optical disc only, the data always needs to be written on both the optical disc and the hard disk. For that purpose, the two types of drives always need to be operated, which is not preferable in view of power saving consideration. The power saving is a particularly important problem for a battery-driven camcorder among other things.
Furthermore, it is not a practical measure to use a DRAM as an alternative cache memory for temporarily storing a huge amount of data such as broadcast data. This is because a DRAM has a relatively small storage capacity for its price.